A common conventional liquid heating device generally includes a cast block 1 made of zinc-aluminum alloy and an electric heating tube 10 and a water conveying tube 11 both contained in the cast block 1. Then the cast block 1 is heated up by the electric heating tube 10, and then the water conveying tube 11 is heated up by the heat of the cast block 1 so that liquid flowing in the water conveying tube 11 is also heated up to become airy vapor. The time required in vaporizing may be 2-3 minutes at least or more than ten minutes at latest depending on the capacity of the electric heating tube 10. If liquid in the tube 11 is to be vaporized in two or three minutes, the heating tube should be large enough to heat up swiftly and accordingly use a large amount of electricity. If liquid is to be heated up in 10-20 minutes, the heating tube can be small to use small amount of electricity, but it takes time, not convenient to use.
The conventional liquid heating device described above uses the electric heating tube 10 for indirectly heating liquid flowing through the water conveying tube 11, having inferior effect in vaporizing due to insufficient heat capacity so that liquid drops may remain at the outlet of the water conveying tube 11, hardly meeting the using standard.
The U.S. Pat. No. 4,246,871 has a water heater 10 surrounding a chamber 20, which then helically located around an outlet 30 so that the water heater 10 may heat the water in the chamber 20. So it is complicated, attaining its object and effect by processing the chamber 20 to surround the water heater 10.
Next, U.S. Pat. No. 5,058,194 has a heating tube 14, and an electric resistance 17 wound on the surface of the heating tube 14. The electric resistance 17 produces high temperature to heat the water in the heating tube 14, impossible to produce steam instantly, as it is an indirect heating mode.